Filling transfer apparatus for bone cement

ABSTRACT

The invention shows a filling transfer apparatus for bone cement with a cylindrical, upwardly open mixing container and a filling transfer piston which can be inserted therein, which is removably connected to the sleeve of a cement injector and which has an opening through which the mixed bone cement can be transferred into the sleeve through a pressing down of the filling transfer piston. In this an ejection piston is inserted in the sleeve and has an aperture in the region of the opening for the through-flowing cement which can be closed by a plug ( 9 ) after the removal of the cement injector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a filling transfer apparatus for bone cementwith a cylindrical mixing container which is upwardly open and to afilling transfer piston which can be inserted therein, which isreleasably connected to the sleeve of a cement injector and which has anopening through which the mixed bone cement can be transferred into thesleeve by a pressing down of the filling transfer piston.

2. Description of the Prior Art

A filling transfer apparatus of this kind is described in detail inEP-A-0 261 182. The latter however has the disadvantage that a fillingtransfer piston which is wetted by liquid bone cement must first bedrawn out of a mixing container and must be disconnected from the actualinjector in order to place on an ejection piston corresponding to theinner crosssection of the injector. In this, liquid bone cement shouldneither be sucked backwards nor spilled nor distributed to thesurroundings.

SUMMARY OF THE INVENTION

The object of the invention is to improve this situation. This object issatisfied in that an ejection piston, which has an aperture in theregion of the opening for the through-flowing cement which can be closedby a plug after the removal of the cement injector, is inserted in thesleeve. This has the advantage that the dynamic seal which is actuallydistributed over a large periphery and is dimensioned for the pressingout is already installed when the bone cement enters into the injector,and that the smaller remaining aperture need only be statically sealed.In addition, the cross-section of the aperture can be matched to theviscosity of a preferred bone cement in such a manner that a backwardflowing is largely prevented. An aperture with a smallest passage areaof less than 50 percent of the inner cross-section of the injectionsleeve already brings about substantial improvements. In the case of arelatively fluid bone cement a passage area of between 25 and 5 percentof the inner cross-section of the injection sleeve has provedadvantageous. In the case of such small apertures of the ejection pistonthe end of a piston rod of an ejection pistol can be provided with aplug which takes over the static sealing during the pressing out of thebone cement because the pressing force for the ejection piston istransferred via a substantially smaller surface than the piston surface.A frontal and possibly elastic shoulder which can adapt to theinclination of the piston surface of the ejection piston suffices as astatic seal and has the advantage that hardened bone cement can besimply removed after use.

A further advantage results when the opening of the filling transferpiston is formed as a nozzle which protrudes into the aperture of theejection piston. The actual restriction of the bone cement then takesplace in the nozzle and only slight taking-along forces arise at theaperture and at the ejection piston during the transfer. When theopening of the nozzle on its outer side lies in contact at the ejectionpiston, it is prevented that the lower side of the ejection piston iswetted by the bone cement. In the removal of the injection sleeve andthe ejection piston then, only a strand of viscous bone cement is stilldrawn between the nozzle and the aperture. A light pre-pressing betweenthe nozzle and the ejection piston can be achieved when the ejectionpiston can be fixed in a lower position in the sleeve, for examplethrough a snap connection which is force and form locked. A bulge whichextends circumferentially in the cylindrical inner surface of the sleeveand which can only be displaced radially outwardly with a larger axialforce at the ejection piston represents a snap connection of this kind.

A further advantage results when the filling transfer piston is blockedin its lower position in such a manner that the sleeve which is filledwith cement and the partially closing-off ejection piston can bereleased from the filling transfer piston in this lower position. If anadditional grip part which can still be gripped in the lower position isattached to the filling transfer piston, then a connection between thesleeve and the filling transfer piston can be released by hand in thelowest position of the filling transfer piston. In a rotational locksuch as in a bayonet lock it suffices to rotate the grip part and thesleeve oppositely to one another. For a rotational lock, instead of agrip part, a rotational securing through projections and recesses can beattached in the lowest position between the filling transfer piston andthe mixing container which transfers a torque from the mixing containerto the filling transfer piston which is required for the release. Sincewith these measures the filling transfer piston need no longer be drawnout in order to release the sleeve, there is also no danger that bonecement is sucked back from the injector into the mixing container.

A grip part has the advantage that relatively large forces can betransmitted to the filling transfer piston for the transfer of the bonecement without a stressing of the connection between the sleeve and thefilling transfer piston thereby arising. In addition the cross-sectionof the aperture and the nozzle can be chosen smaller when large forcescan be transmitted to the filling transfer piston.

As concerns the handling, it is advantageous to provide the same kind oflock, for example a bayonet lock, between the sleeve and the fillingtransfer piston as between the sleeve and the ejection pistol. Thesleeve with the bone cement remains in the same hand without a change ofgrip after the release from the filling transfer piston and can beplaced onto the ejection pistol with an opposite movement.

A further functional advantage arises when the sleeve has a conicaltransition to a distributor tube and when this cone is repeated in theejection piston and in the aperture as a nozzle. With this measure theoutflow resistance to the distributor tube is lowered and the entirevolume is pressed out into the distributor tube. In addition a stableguidance of the ejection piston is achieved when the force applicationof the piston takes place practically above the piston surface and abovethe sealing surface between the ejection piston and the sleeve. A shortguide surface of the ejection piston in the sleeve, which can coincidewith the sealing surface, suffices since with this suspension at thepiston rod the ejection piston shows no tendency to tilt.

For practical reasons the mixing container can be executed as atransport container for one of the components of the bone cement so thata part which is designed as a throw-away part anyway fulfils a multiplefunction. A component of the bone cement in powder form can be enclosedin the mixing container for the transport by a cover or a tear-off foil.After the removal of the cover or the tear-off foil further componentscan be added and mixed by hand with a spatula. Then the filling transferpiston, on which the injector sleeve and the ejection piston werepreviously delivered in a pre-mounted condition, is placed on. After themixing the operating personnel need only introduce and press down thefilling transfer piston, release the sleeve from the filling transferpiston and place it on the ejector pistol, and this without applyingsticky bone cement residues to the surfaces which can be gripped fromthe outside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically, a view of a filling transfer pistonwith a grip part which has longitudinal ribs for the guidance of theactual piston;

FIG. 2 illustrates schematically, a longitudinal section through amixing container which can initially be used as a transport containerand after the mixing as a cylinder for the filling transfer piston inaccordance with FIG. 1;

FIG. 3 illustrates schematically, a longitudinal section through acement injector, in the sleeve of which an ejection piston with acentral aperture is pre-mounted;

FIG. 4 illustrates schematically, a longitudinal section through afilling transfer piston of FIG. 1 in which an arrangement in accordancewith FIG. 3 can be inserted with a bayonet lock;

FIG. 5 illustrates schematically in a longitudinal section, a fillingtransfer piston with a cement injector in its lowest position in themixing container; and

FIG. 6 illustrates schematically in a longitudinal section, the cementinjector of FIG. 5 after the placing on onto an ejector pistol.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT

A filling transfer apparatus for bone cement with a cylindrical,upwardly open mixing container 1 and with a filling transfer piston 2which can be inserted therein, which is removably connected to thesleeve 4 of a cement injector 3 and which has an opening 5 through whichthe mixed bone cement 6 can be transferred into the sleeve 4 through apressing down of the filling transfer piston 2 is illustrated in thefigures. Inserted in the sleeve 4 in this is an ejection piston 7 whichhas an aperture 8 in the region of the opening 5 for the through-flowingcement which can be closed with a plug after the removal of the cementinjector 3.

The reference symbols in the figures are used for similar concepts.Since such parts as the mixing container 1, the lid 21, the fillingtransfer piston 2, the cement injector 3 with the sleeve 4 and with theejection piston 7 are throw-away parts with large production numbers,these are as a rule manufactured of thermoplastics in injection mouldingmachines.

FIGS. 1 and 2 show a filling transfer piston 2 with an associated mixingcontainer 1. The actual piston with the piston surface 26 is executedwith thin walls and with a grip part 13 which consists of a tube sectionwhich is substantially taller than the mixing container 1 and which endsin a laterally protruding ring 22 at which the filling transfer pistoncan be pressed down by hand to the base of the mixing container 1.Longitudinal ribs 23 are distributed at the tube section over theperiphery parallel to the longitudinal axis 28 and prevent, as guides,an inclined position of the piston surface 26 and its sealing edge inthe mixing container. Two windows 24, which are displaced by 180°, areprovided in the lower part of the tube section in order to be able tospout out in each case a pin 25 for a bayonet lock on a further inwardlylying ring 27 at laterally deformable tool punches.

The mixing container 1 is shown as a transport container which is closedby a lid 21 via a snap connection 30 in order to store and to transportcomponents 17 of bone cement in powder form. For the production of theactual liquid bone cement the lid 21 is torn open at the side andremoved. Then a liquid component is added to the powder component 17from a separate vessel and the compound is stirred during apredetermined reaction time and mixed as uniformly as possible. The thusresulting bone cement 6, which is flowable for a limited time, must nowbe transferred into a cement injector 3.

The actual cement injector 3, which has a sleeve 4 with a conicaltransition 18 and a distributor tube 19, is shown in FIG. 3. The lowerboundary of the sleeve 4 is reinforced outwardly and has four cut-outsfor a bayonet lock 15. An ejection piston 7, of which the piston surfaceis matched to the inclination of the conical transition 18, is fixed ina lower position 16 by means of a slight modification (not shown) of theinner diameter of the sleeve 4. The ejection piston 7 has an aperture 8in the centre which is matched to the outer dimensions of a nozzle 12(FIG. 4). The ejection piston 7 receives a high stiffness against highpressing-on pressures through a support ring 31 and radial ribs 32. Thefixing of the ejection piston 7 at the lower position 16 is dimensionedin such a manner that it can move upwardly only in the presence of alarger axial force.

The elements which are matched to the sleeve 4 and to the ejectionpiston 7 of the cement injector 3 are visible in FIG. 4. A guide ring 27which is formed on at the piston base corresponds with its outerdiameter to the inner diameter of the sleeve 4 and has two pins 25 whichtogether with the cut-outs at the lower end of the sleeve 4 form abayonet lock 15 which determines the axial position between the sleeve 4and the filling transfer piston 2. Corresponding to this position and tothe lower position 16 of the ejection piston 7 the opening 5 of thefilling transfer piston 2 is formed to a nozzle 12 which protrudes intothe ejection piston 7 and which with the actuation of the bayonet lock15 lies in contact at the ejection piston 7 with a shoulder 29. Thecement injector 3 with the ejection piston 7 and the filling transferpiston 2 are put together prior to the introduction of the fillingtransfer piston 2 into the mixing container 1 and locked relative to oneanother via the bayonet lock 15.

The locked unit of the filling transfer piston 2 and the cement injector3 is gripped at the grip part 13 and pushed in from above into a mixingcontainer 1 with fresh bone cement 6. When the bone cement 6 isencountered, the latter must be displaced through the mouth 12 into thecement injector 3. Corresponding to the diameter of the mouth 12 and tothe momentary viscosity of the bone cement a corresponding axial forcemust be applied at the ring 22 until the filling transfer piston 2, asshown in FIG. 1, has reached the base of the mixing container 1. In FIG.5 the nozzle 12 thrusts completely through the ejection piston 7 so thatthe bone cement 6 which flows into the sleeve 4 is uniformly distributedunder the action of gravity in the sleeve 4 and slowly fills the latter,with the air above it being driven out through the distributor tube 19.

When the base is reached the bone cement 6 has been completelytransferred into the cement injector 3 with the exception of a residualamount in the nozzle 12 and extends up into the distributor tube 19. Inthe case of a very fluid bone cement 6 a closure cap (not shown here)can be applied to the distributor tube 19 after the transfer in order toprevent a subsequent flowing of bone cement during the separation of thebayonet lock 15 between the filling transfer piston 2 and the cementinjector 3. Beneath the ejection piston 7 there is a cavity 33 which isventilated so well that air for a constriction and separation of thebone cement 6 in the aperture 8 can flow in when the bayonet lock 15 isreleased and when the cement injector 3 is pulled off at the partitionlocation between the aperture 8 and the shoulder 29. For the release ofthe bayonet lock 15 the sleeve 3 is gripped at its upper region with onehand, while a corresponding counter-force is applied to the grip part13, 22 with the other hand.

The cement injector 3 which has been drawn off is pushed onto an ejectorpistol 11 as shown in FIG. 6. The latter has a piston rod 10 which canbe moved out and onto which a plug 9 has been pushed on in order to sealoff 20 the aperture 8 with the plug 9 and to transmit the ejectionforces to the ejection piston 7. The piston rod 10 experiences, througha trigger lever 35 which is moved towards a pistol grip 34, a forwardthrust movement which is strongly geared down in order to produce alarge ejection force. For the transmission of a larger ejection force,pins engage at all four cut-outs of the sleeve 4 in order to form thebayonet lock 15. The large ejection force is necessary in order toovercome the cross-sectional reduction to the diameter of thedistributor tube 19 and the friction at the distributor tube 19 and thesleeve 4. The pins are braced in a connection piece 36 which is matched,like the guide ring 27 in the filling transfer piston 2, to the innerdiameter of the sleeve 4 in order to give the latter an orientation inthe direction of the forward thrust movement of the piston rod 10.

What is claimed is:
 1. A filling transfer apparatus for bone cementcomprising a cylindrical, upwardly open mixing container and a fillingtransfer piston that can be inserted therein, which is removablyconnected to a sleeve of a cement injector and which has an openingthrough which the mixed bone cement may be transferred into the sleevethrough a pressing down of the filling transfer piston, wherein anejection piston is inserted in the sleeve and has an aperture in aregion of the opening for the through-flowing cement that can be closedby a plug after the removal of the cement injector, and wherein thesleeve and the filling transfer piston are connectable through arotational lock.
 2. A filling transfer apparatus in accordance withclaim 1 wherein the smallest passage surface in the aperture correspondsto less than 50 percent of the inner cross-sectional surface of thesleeve.
 3. A filling transfer apparatus in accordance with claim 2wherein the smallest passage surface in the aperture corresponds tobetween 25 and 5 percent of the inner cross-sectional surface of thesleeve.
 4. A filling transfer apparatus in accordance with claim 1wherein the plug is formed by an end of a piston rod as a constituent ofan ejector pistol which can be releasably connected to the sleeve.
 5. Afilling transfer apparatus in accordance with claim 1 wherein theopening is formed out as a nozzle which protrudes into the aperture ofthe ejection piston.
 6. A filling transfer apparatus in accordance withclaim 1 wherein the ejection piston can be fixed at a lower position inthe sleeve.
 7. A filling transfer apparatus in accordance with claim 1wherein the filling transfer piston has a grip part which enables amoving of the filling transfer piston by hand.
 8. A filling transferapparatus in accordance with claim 7 wherein the grip part is providedwith longitudinal ribs which lie in contact in the longitudinaldirection at the mixing container in order to provide a guidance for thefilling transfer piston.
 9. A filling transfer apparatus in accordancewith claim 1 wherein the sleeve is connectable with the same kind tolock both of the ejection piston and to the ejector pistol.
 10. Afilling transfer apparatus in accordance with claim 1 wherein thefilling transfer piston is blocked against a rotation at least in itslowermost position in the mixing container.
 11. A filling transferapparatus in accordance with claim 1 wherein the mixing container isexecuted as a closeable transport container for at least one of thecomponents of a bone cement to be mixed.
 12. A filling transferapparatus in accordance with claim 11 wherein the mixing container canbe closed with a lid or with a film for the transport of components ofbone cement.
 13. A filling transfer apparatus for bone cement comprisinga cylindrical, upwardly open mixing container and a filling transferpiston that can be inserted therein, which is removably connected to asleeve of a cement injector and which has an opening through which themixed bone cement may be transferred into the sleeve through a pressingdown of the filling transfer piston, wherein an ejection piston isinserted in the sleeve and has an aperture in a region of the openingfor the through-flowing cement that can be closed by a plug after theremoval of the cement injector, and wherein the sleeve is connectablewith the same kind of lock both to the ejection piston and to theejector pistol.
 14. A filling transfer apparatus for bone cementcomprising a cylindrical, upwardly open mixing container and a fillingtransfer piston that can be inserted therein, which is removablyconnected to a sleeve of a cement injector and which has an openingthrough which the mixed bone cement may be transferred into the sleevethrough a pressing down of the filling transfer piston, wherein anejection piston is inserted in the sleeve and has an aperture in aregion of the opening for the through-flowing cement that can be closedby a plug after the removal of the cement injector, and wherein thefilling transfer piston is blocked against a rotation at least in itslower-most position in the mixing container.
 15. A filling transferapparatus for bone cement comprising a cylindrical, upwardly open mixingcontainer and a filling transfer piston that can be inserted therein,which is removably connected to a sleeve of a cement injector and whichhas an opening through which the mixed bone cement may be transferredinto the sleeve through a pressing down of the filling transfer piston,wherein an ejection piston is inserted in the sleeve and has an aperturein a region of the opening for the through-flowing cement that can beclosed by a plug after the removal of the cement injector, and whereinthe grip part is provided with longitudinal ribs that lie in contact inthe longitudinal direction at the mixing container in order to provide aguidance for the filling transfer piston.